In recent years, a display element of an image display device such as a television device is shifting from a conventional CRT display device to a thin display device using a thin display element such as a liquid crystal panel and a plasma display panel. This enables the image display device to have a reduced thickness. A liquid crystal panel used for a liquid crystal display device does not emit light, and thus a backlight unit is required as a separate lighting device. Backlight units can be broadly categorized into two types, i.e. a direct-type backlight unit and an edge-type backlight unit, according to its structure. It is preferable to use the edge-type backlight unit to further reduce the thickness of the liquid crystal display device. Patent Document 1 describes a known edge-type backlight unit. The edge-type backlight unit described in Patent Document 1 includes LEDs as light sources and an LED board on which the LEDs are mounted. The LED board faces a light entrance surface of the light guide plate.